From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965244AbVKBVRV (ORCPT ); Wed, 2 Nov 2005 16:17:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965247AbVKBVRU (ORCPT ); Wed, 2 Nov 2005 16:17:20 -0500 Received: from gate.crashing.org ([63.228.1.57]:38835 "EHLO gate.crashing.org") by vger.kernel.org with ESMTP id S965244AbVKBVRU (ORCPT ); Wed, 2 Nov 2005 16:17:20 -0500 Subject: Re: [PATCH] Don't touch USB controllers with MMIO disabled in quirks From: Benjamin Herrenschmidt To: Linus Torvalds Cc: Alan Stern , Paul Mackerras , akpm@osdl.org, David Brownell , Greg Kroah-Hartman , linux-kernel@vger.kernel.org In-Reply-To: References: Content-Type: text/plain Date: Thu, 03 Nov 2005 08:13:54 +1100 Message-Id: <1130966034.20136.52.camel@gaston> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > But an alternative strategy (which might be very sensible) is to forget > about the handoff entirely, and just shut down the bus master flag > unconditionally. Just make sure that the eventual driver will reset the > controller before it re-enables bus mastering. Unfortunately, I know quite a few devices (including USB controllers) that will react badly to the bus master flag being just cleared like that. By badly, I mean it ranges from simply ignoring it and happily continuing whatever bus master was being done, to completely screwing up and crapping all over your memory/bus. > That would seem to be the simplest possible "handoff". The only danger is > that I could imagine that there would be controllers out there that get > really confused (ie "I'm not going to play nice any more") if we shut them > up that way. I suspect with the IO/MEM enable test fix we did, it shoul work fine in practice for all cases. Let's address the "potential" issues if they happen to show up in real life, which I doubt. Ben.